4 floppy disk drives on a PC?

Tony, Nice discussion of the various floppy formats. One point you didn't mention is that the standard PC format has 9 sectors per track, while the DEC RX50 has 10 sectors per track. So in fact the RX50 does not have the same capacity as the double sided 48tpi PC floppies -- it has 10% more because of the higher sector count. PC floppies can read and write RX50 format, given a 96tpi capable drive. You can do it under DOS by using direct BIOS calls (int 13); under Linux, by setting the drive parameters to match the RX50 format. In addition, the RX50 logical block number to c/h/s mapping is odd. There is a 2:1 interleave, which is reasonable enough. Harder to explain is that logical block 0 is in cylinder 1, and cylinder 0 contains the last 10 blocks. I can supply details and sample code if anyone is interested (or you can find my utility "rstsflx" which has all this -- John Wilson's file server has a copy, as does Johnny Billquist if I remember right. paul